Scheduled peer power save mode

ABSTRACT

Embodiments of scheduled peer power save systems, devices, and methods are disclosed. For example, methods of saving power for stations configured to communicate via a direct link are provided. Embodiments of scheduled peer power save systems, devices and methods are disclosed. For example, methods of saving power for stations configured to communicate via a direct link are provided. In one embodiment, among others, a method comprises waking up, at a station and peer station, before a scheduled wakeup interval. The scheduled wakeup interval is defined relative to common timing reference at the station and the peer station. Further, in the absence of a service period between the station and the peer station, the station and the peer station stay awake until at least a predefined time period has elapsed or a predefined number of idle slots have elapsed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/363,740,filed Jan. 31, 2009, which claims priority to U.S. ProvisionalApplication having Ser. No. 61/025,417, filed on Feb. 1, 2008, and U.S.Provisional Application having Ser. No. 61/025,415, also filed on Feb.1, 2008, all of the above which is also incorporated herein by referencein their entirety.

TECHNICAL FIELD

The present disclosure is generally related to communication systems,and, more particularly, is related to wireless communication systems andmethods.

BACKGROUND

Wireless communication systems are widely deployed to provide varioustypes of wireless communication, such as voice, data, and so on, betweenvarious devices (also referred to as stations) such as cell phones,laptop computers, cameras, servers, desktop computers, etc. IEEE 802.11is a set of standards for wireless local area network (WLAN)communication between the devices, which is also sometimes referred toas wireless fidelity (WiFi). The devices fall into one of twocategories: access points (APs) and clients. APs, normally routers, arebase stations for the wireless network that connect to a wired networkinfrastructure. Clients are typically end devices, which are referred toas stations.

Wireless communication has provided users with the ability tocommunicate with wireless devices without the constraints of a wiredconnection. To further facilitate mobility, many wireless devices, suchas cell phones, laptop computers, cameras, etc., also utilize mobilepower sources, such as batteries. As many of these wireless devicesutilize battery power, conserving power to extend battery life hasemerged as a priority.

SUMMARY

Embodiments of scheduled peer power save systems, devices and methodsare disclosed. For example, methods of saving power for stationsconfigured to communicate via a direct link are provided. In oneembodiment, among others, a method comprises waking up, at a station andpeer station, before a scheduled wakeup interval. The scheduled wakeupinterval is defined relative to a common timing reference at the stationand the peer station. Further, in the absence of a service periodbetween the station and the peer station, the station and the peerstation stay awake until at least a predefined time period has elapsedor a predefined number of idle slots have elapsed.

Other systems, methods, features, and advantages of the presentdisclosure will be or become apparent to one with skill in the art uponexamination of the following drawings and detailed description. It isintended that all such additional systems, methods, features, andadvantages be included within this description, and be within the scopeof the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the disclosed systems and methods can be betterunderstood with reference to the following drawings. The components inthe drawings are not necessarily to scale, emphasis instead being placedupon clearly illustrating the principles of the disclosed systems andmethods. Moreover, in the drawings, reference numerals designatecorresponding parts throughout the several views.

FIG. 1 is a block diagram of an exemplary communication environment inwhich embodiments of scheduled peer power save mode systems and methodscan be implemented.

FIG. 2 is a block diagram that illustrates an embodiment of a scheduledpeer power save mode (PSM) system embodied in one of the devices shownin FIG. 1.

FIG. 3 is a schematic diagram of a general media access control (MAC)frame format defined in IEEE 802.11.

FIG. 4 is a schematic diagram of a frame control field of the generalMAC frame format defined in IEEE 802.11 and depicted in FIG. 3.

FIGS. 5-19 are flow charts that illustrate several embodiments ofmethods executed by the scheduled peer PSM system shown in FIGS. 1 and2.

DETAILED DESCRIPTION

Disclosed herein are various embodiments of scheduled peer power savemode (PSM) systems and methods wherein the battery life of a wirelessdevice can be improved for at least the reason that the wake time isreduced when compared to conventional techniques. In scheduled peer PSM,a station and a peer station are configured to communicate over a directlink. The station and the peer station wake up according to a periodicschedule to see if the other station has traffic for it, and possibly totransmit traffic to the other station. During the scheduled peer listenintervals (also referred to as wakeup intervals), the station and thepeer station can start service periods in which traffic is sent betweenthe stations depending on whether they have traffic to send (e.g.transmit) to each other. The service periods may be UnscheduledAsynchronous Power Save Delivery (U-APSD) service periods, which arealso referred to as unscheduled service periods. Other types of serviceperiods may also be used. Also, depending on the amount of traffic theyhave to send, the stations can adjust the wakeup schedule and/or theduration of the service period. For the same traffic stream, the serviceperiods will contain more frame exchanges when the time between wakeupintervals increases (e.g., the content of the service intervalstypically increases when the time between the wakeup intervalsincreases). Hence, in scheduled peer PSM, a station may be able totransmit buffered traffic to a peer station instead of relying on theaccess point (AP) to perform this function. Further, in scheduled peerPSM, both stations may be able to be in a power save mode at the sametime.

Such scheduled peer PSM systems, devices, and methods are describedbelow in the context of IEEE 802.11 compliant communication systems,though the principles described herein can be extended to othercommunication systems and protocols and hence are not so limited. Thisdescription is written with reference to public documents IEEE DraftP802.11z_D0.1.doc, IEEE document IEEE802.11-2007.pdf (IEEE Std802.11™-2007) and WFA document WMM_Specification_1_1.doc (WMM™(including WMM™ Power Save) Specification version 1.1), which are allhereby incorporated by reference in their entirety.

FIG. 1 is a block diagram of an exemplary communication environment 100in which embodiments of scheduled peer PSM can be implemented. Thecommunication environment 100 comprises a plurality of wireless andwired devices, one or more of which may be configured to operate as awireless and wired device. One or more of the devices shown in FIG. 1may incorporate scheduled peer PSM systems and methods, as describedfurther below. Exemplary wireless devices include a cell phone 102, alaptop computer 104 (which, along with other devices, may communicatewith the cell phone 102 in a direct link mechanism as represented bydirect link 114), and a digital camera 106. The wired devices (e.g.,with wireless capability) include a personal computer (PC) 108, atelevision 110, and a server 112. In the communication environment 100shown in FIG. 1, the cell phone 102 is in communication (e.g., radiofrequency communication) with the laptop computer 104 and the PC 108 viaan AP 120, and the server 112 is in communication with the television110 via the AP 120. Also, the digital camera 106 is in communicationwith the laptop 104 and the PC 108 via the AP 120. For instance, suchcommunications may be used to load pictures from the digital camera 106to the PC 108. For illustrative purposes, the cell phone 102 is shown asan appliance that embodies an embodiment of the scheduled peer PSMdevice 200 as a station, and the laptop 104 is shown as an appliancethat embodies an embodiment of the scheduled peer PSM device 200 as peerstation. Wireless direct links 114 may be instantiated between any ofthe devices shown in FIG. 1.

Note that communication between the various devices may employ one ormore of a plurality of protocols, including 802.11 (e.g., 802.11a,802.11b, 802.11e, 802.11g, 802.11n, 802.11z), WiMax, Ultra-Wide Band(UWB), Bluetooth, among other technologies. Additionally, although thecommunication environment 100 is shown as a basic service set (BSS)configuration, in some embodiments, communication among one or moredevices may be implemented using peer-to-peer (also known as adhoc inmany wireless technologies) communication in lieu of or in addition tocommunication through the AP 120. In FIG. 1, the cell phone 102 andlaptop computer 104 can communicate peer-to-peer over the direct link114.

FIG. 2 is a block diagram that illustrates an embodiment of a scheduledpeer PSM device 200 implemented in the cell phone 102 shown in FIG. 1,with the understanding that other devices may embody the scheduled peerPSM device 200 in addition to, or in lieu of, the cell phone 102. Notethat the devices shown in FIGS. 1 and 2 are exemplary in nature, andthat the scheduled peer PSM device 200 may be implemented in any one ofa plurality of different devices or appliances, including computers(desktop, portable, laptop, etc.), consumer electronic devices (e.g.,multi-media players, music players, portable sound recording devices,digital radio devices), cell phones, smart phones, compatibletelecommunication devices, personal digital assistants (PDAs), globalpositioning system (GPS) navigation systems, or any other type ofnetwork devices, such as printers, fax machines, scanners, hubs,switches, routers, set-top boxes, video game consoles, receivers,webcams, digital cameras, digital camcorders, televisions withcommunication capability, projectors, video servers, network attachedstorage (NAS) drives, roadside communication systems, cars, robots, etc.Scheduled peer PSM may be applied inside a house, a living room, anoffice, on a street, in a yard, a car, between a car and a roadsidesystem, or in any one of a variety of other environments.

The scheduled peer PSM device 200 can be implemented using digitalcircuitry, analog circuitry, or a combination of both, and is embodiedin one embodiment using a combination of hardware and software. As tohardware, one or more components of the scheduled peer PSM device 200can be implemented with any or a combination of the followingtechnologies, which are all well known in the art: a discrete logiccircuit(s) having logic gates for implementing logic functions upon datasignals, an application specific integrated circuit (ASIC) havingappropriate combinational logic gates, a programmable gate array(s)(PGA), a field programmable gate array (FPGA), etc.

In one embodiment, the scheduled peer PSM device 200 comprises a memory202, a host processor (or media access controller in some embodiments)204 executing code (e.g., a driver) referred to also as an upper MAC206, and a network card 208 (e.g., network interface card or wirelesscard) coupled to the host processor 204, the network card 208 comprisinga processor or media access controller 209 executing code referred to asa lower MAC 210, a baseband processor 211 coupled to the processor 209,a transceiver 212 coupled to the baseband processor 211, and an antenna213 coupled to the transceiver 212. Note that the above-describedcomponents of the scheduled peer PSM device 200 are also collectivelyreferred to as a station. In some embodiments, a station may compriseadditional or different components. Further, in some embodiments, thelower MAC 210 can be incorporated into the baseband processor 211. Thetransceiver 212 comprises in one embodiment such well-known transceivercomponents including filters, amplifiers (e.g., power amplifiers,switches, etc.). The host processor 204 and processor (or media accesscontroller) 209 may each be embodied as a digital signal processor(DSP), a microprocessor, a general purpose processor, or an applicationspecific integrated circuit (ASIC), among others devices. One havingordinary skill in the art should appreciate that additional componentsnot shown can be used (e.g., a host processor interface, various busses,etc.), yet which are omitted for brevity.

In one embodiment, preparation, transmission, and reception of frames,as well as the determination of signal strength, is under the control ofthe lower MAC 210 as executed by the processor 209. In some embodiments,control of the aforementioned functionality is solely by either theupper MAC 206 or the lower MAC 210, and in some embodiments, theexecution of the MACs 206 and 210 may be implemented via a singleprocessor or on two or more processors. In some embodiments,functionality of the upper and lower MACs 206 and 210 may becollectively performed in a single MAC.

In one embodiment, the upper MAC 206 and lower MAC 210 each comprisesoftware (e.g., firmware) residing on the respective processors 204 and209, respectively, and the software is executed by a suitableinstruction execution system. In some embodiments, functionality of theupper MAC 206 and lower MAC 210 may comprise software stored in memory(e.g., memory 202) or other computer readable medium (e.g., optical,magnetic, semiconductor, etc.), and executed by the host processor 204or other processor.

Wireless LANs are generally implemented according to the standarddefined by the ISO/IEC 8802-11 international standard (IEEE 802.11) forwireless systems operating in the 2.4-2.5 GHz ISM (industrial,scientific and medical) band, which is also referred to as IEEE Std802.11™-2007. FIG. 3 illustrates the general MAC frame format defined inIEEE 802.11. Each MAC frame includes a MAC header, a variable lengthframe body and a frame check sequence (FCS). As shown, the MAC headerincludes Frame Control, Duration/ID, Address 1, Address 2, Address 3,Sequence Control, Quality of Service (QoS) Control and Address 4 fields.A frame check sequence (FCS) is appended after the frame body. Theaddress fields in MAC frame format are used to indicate the BasicService Set identifier (BSSID), Source address (SA), Destination Address(DA), Transmitter Address (TA), and Receiver Address (RA), depending onthe direction of the frame (station to station, station to AP, AP tostation, or AP to AP, respectively). Thus, when receiving data framestransmitted in the wireless LANs, stations operating in a service setcan detect the packets transmitted over a wireless media (WM) anddetermine the intended recipient in accordance with the destinationinformation thereof. A station waiting for data frames needs to bepowered in order to receive packets transmitted to the station.

However, since most stations in the wireless network are mobile deviceswhich may be battery powered, power management becomes an importantconsideration in performance analysis. IEEE 802.11 provides a mechanismto support establishment and maintenance of the power management (PM)mode of a station, wherein a station may be in one of two differentpower states, awake and doze. The station in an awake state (alsoreferred to as an awake mode) is fully powered, while the station indoze state is not able to transmit or receive and consumes very lowpower.

Unscheduled Asynchronous Power Save Delivery (U-APSD) is a mechanism forIEEE 802.11-based systems that was developed to help wireless devicesconserve power. According to U-APSD, the station sends a trigger frameto the AP when the AP has indicated that it has buffered traffic for thestation. The trigger frame is then typically acknowledged by the AP. Thestation remains awake after sending the trigger frame. At some timeafter receiving the trigger frame, the AP responds by sending buffereddownlink traffic to the station. On the final downlink frame, the accesspoint may set an End Of Service Period (EOSP) bit, which indicates tothe station that the service period has ended and that the station canreturn to a doze state, where at least one of the active componentsutilized during normal operation is deactivated during a period ofcommunicative inactivity. The rules governing the U-APSD service periodare described in more detail in subclause 11.2.1.4 of IEEE Std802.11™-2007 or in subclause 3.6 of WMM™ (including WMM™ Power Save)Specification version 1.1.

Scheduled peer PSM is a power save mode that can be used by a stationand a peer station that support Tunneled Direct Link Setup (TDLS) (IEEE802.11z). TDLS is characterized by the fact that the signaling framesare encapsulated in data frames, which allows them to be transmittedthrough an AP transparently. Therefore, a direct link can be setup usingany AP. The AP does not need to be direct link aware, nor does it haveto support any of the capabilities that will be used on the direct link.TLDS also includes an option to enter scheduled peer PSM while remainingon the direct link, so that the station can enter a doze state while thedirect link remains logically in place.

Stations capable of supporting scheduled peer PSM may signal thiscapability by setting a Peer PSM capability bit to 1 in the ExtendedCapabilities Information Element in the body of a management frame. ThePeer PSM capability bit set to 0 indicates that the station does notsupport this capability. Section 7.3.2.27 of IEEE documentIEEE802.11-2007.pdf describes the Extended Capabilities InformationElement in further detail.

FIGS. 5-19 are flow charts illustrating various methods of saving powerfor stations configured to communicate via a direct link. One or more ofthe methods include waking at a station and/or a peer station accordingto a periodic wakeup schedule for one or more scheduled wakeupintervals. The station and/or peer station transmit data frames to eachother over a direct link during the scheduled wakeup intervals, andduring the non-wakeup intervals, the station and/or peer station mayenter a doze state. In some embodiments, the wakeup schedule is adjustedor terminated to increase the amount of time the station and/or the peerstation may spend in a doze state to conserve power. In the doze state,it is not possible for the station to receive any frames on the wirelessmedium.

One or more of the methods is executable by the devices illustrated inthe communication environment 100 depicted in FIG. 1. For example, thecell phone 102, the laptop computer 104, and the AP 120 of FIG. 1 mayembody the station, the peer station, and the AP, respectively,described below. Further, in some embodiments, the scheduled peer PSMdevice 200 described above with respect to FIG. 2 may be configured as astation or a peer station. In other words, in some embodiments, thestation or the peer station store modules, segments, or portions of codeincluding one or more executable instructions for execution by aprocessor to implement specific logical functions or blocks of theembodiments of the methods described below.

FIG. 5 is a flow chart that illustrates a first embodiment of a methodof saving power for stations configured to communicate via a directlink. In FIG. 5, the method 500 includes blocks 510, 520, 530, 540, 550,560, and 570. In block 510, a wakeup schedule request frame thatincludes a proposed wakeup schedule is transmitted from a station to apeer station. In some embodiments, the station is not in a power savemode with respect to the peer station and the peer station is not in apower save mode with respect to the station when the wakeup schedulerequest frame including the proposed wakeup schedule is transmitted fromthe station to the peer station.

An exemplary wakeup schedule request frame may include some or all ofthe information shown below in Table 1.

TABLE 1 Exemplary Wakeup Schedule Request Frame fields Order Field Notes1 Link Identifier The Link Identifier identifies the direct link 2Wakeup The wakeup schedule field defines a periodic Schedule wakeupschedule

The link identifier field of the exemplary wakeup schedule request framein Table 1 may identify a direct link through the station MAC address,the peer station MAC address, and the basic service set identifier(BSSID), which is the AP MAC address.

The wakeup schedule field of the exemplary wakeup schedule request framedefines a periodic wakeup schedule. Table 2 illustrates an exemplaryembodiment of the subfields of the wakeup schedule field of a wakeupschedule request frame. The wakeup interval length subfield indicatesthe length of the wakeup interval. The wakeup interval offset subfieldindicates the offset of the start of the wakeup interval relative to theTBTT. In some embodiments, a periodic wakeup schedule may be defineddifferently from the exemplary embodiment illustrated in Table 2.

TABLE 2 Exemplary Wakeup Schedule subfields Order Information Notes 1Wakeup 2 octet field that indicates the length of the wakeup Intervalinterval in units of μs (unsigned integer). Length 2 Wakeup 4 octetfield that indicates the offset of the beginning Interval of the wakeupinterval relative to the TBTT, in units Offset of μs (signed integer).

The wakeup intervals are scheduled periods during which both the stationand the peer station are to be in an awake state during which they canreceive or transmit frames on the wireless medium. At other times(outside of the wakeup intervals), the station and the peer station mayenter a doze state during which they can not receive frames on thewireless medium. The wakeup intervals are defined as a duration and aperiodicity relative to a shared time reference, such as the timingsynchronization function (TSF) or the target beacon transmission time(TBTT). The TSF is a timing reference that is shared amongst devicesassociated with the same AP within the same basic service set (BSS), andthe TBTT is defined based on the TSF. The AP includes a TSF timestamp inevery beacon frame it transmits, which can be used by stations in theBSS to synchronize their internal TSF timer. Since both the station andthe peer station are associated with the same AP, which regularlytransmits beacons to the stations, both stations have the same notion ofthe TSF and therefore the TBTT.

In some embodiments, the wakeup intervals are defined as a predefinednumber of idle slots instead of a fixed amount of time. The idle timeslots are counted/determined according to the channel access rules thatgovern access to the channel. For example, in the absence of trafficexchanged between the station and the peer station, the station mayenter a doze state after predefined number of idle slots have occurred.In some embodiments, the number of idle slots defining the wakeupinterval may be negotiable between the station and the peer stationinstead of being predefined. In some embodiments, the number of idleslots defining the wakeup interval may be equal to a minimum contentionwindow (CWmin). In some embodiments, the number of idle slots definingthe wakeup interval may be related to an average contention window.Examples of channel access rules include the distributed coordinationfunction (DCF) and enhanced distributed channel access (EDCA), both ofwhich are defined in IEEE Std 802.11-2007. In some embodiments, theCWmin and the average contention window are defined according to thechannel access rules.

In some embodiments, the peer station may be in a doze state withoutperiodic wakeup when the wakeup schedule request frame is transmitted tothe peer station from the station. Hence, at that point, it is unknownat the station if and when the peer station is ready to receive a frameon the wireless medium. The wakeup schedule request frame is transmittedto the peer station through the AP in block 510 in this case. In otherembodiments, the peer station may not be in a power save mode, in whichcase the wakeup schedule request frame can be transmitted via the directlink in block 510.

In block 520, the wakeup schedule request frame is received at the peerstation, and the peer station determines whether the proposed wakeupschedule is acceptable. The acceptability of the proposed wakeupschedule may be determined based on a variety of criteria. For example,the proposed wakeup schedule may be acceptable or not acceptabledepending on the power level of the peer station. If the peer station islow on battery power, then it may not be appropriate for the peerstation to begin a wakeup schedule that requires a frequent wakeup, andthus, under those conditions, the peer station may determine that theproposed wakeup schedule is not acceptable.

In block 530, when the proposed wakeup schedule in the wakeup schedulerequest frame is determined acceptable by the peer station, a wakeupschedule response frame is sent from the peer station to the station.The wakeup schedule response frame is sent via the direct link. Thewakeup schedule response frame indicates that the proposed wakeupschedule is accepted or it acknowledges the proposed wake up schedule.An exemplary wakeup schedule response frame may include the informationshown in Table 3.

TABLE 3 Exemplary Wakeup Schedule Response Frame Fields Order FieldsNotes 1 Link Identifier The Link Identifier field identifies the directlink 2 Wakeup The Wakeup Schedule field defines a periodic Schedulewakeup schedule

The link identifier field may identify a direct link through the stationMAC address, the peer station MAC address and the basic service setidentifier (BSSID), which is the AP MAC address. The wakeup schedulefield may be omitted from the wakeup schedule response frame when thewakeup schedule request frame included an acceptable wakeup schedule.

In some embodiments, the station enters an awake state immediately aftersending the wakeup schedule request frame in block 510 and possiblybefore the station receives the wakeup schedule response frame sent fromthe peer station.

In block 540, a frame including a power management (PM) bit set istransmitted from the station to the peer station. The PM field is 1 bitin length and indicates the PM mode of the station. The PM field isincluded in the frame control field of the MAC header, as illustrated inFIG. 4. The value of the PM bit indicates the mode of the station afterthe successful completion of the frame exchange sequence. A value of 1indicates that the station is in a power save mode. A value of 0indicates that the station is in an active (constantly awake) mode. Theframe including the PM bit set in block 540 includes the PM bit set to1, to indicate that the station is in a power save mode.

In block 550, the station wakes up at or before a scheduled wakeupinterval according to the accepted wakeup schedule. In other words, thestation enters an awake mode at or before a scheduled wakeup interval.The station may have formerly been in a doze state. The station iscurrently in a power save mode that includes periodically waking up forat least the negotiated wakeup intervals.

In block 560, a frame including a PM bit set is transmitted from thepeer station to the station. The frame including the PM bit set includesthe PM bit, which is illustrated in FIG. 4, set to 1 to indicate thatthe peer station is in a power save mode. The frame including the PM bitset to 1 may be transmitted during an awake window as agreed upon inblock 530.

In block 570, the peer station wakes up at or before the scheduledwakeup intervals. In other words, the peer station enters an awake modeat or before the scheduled wakeup interval that was scheduled accordingto the negotiated wakeup schedule.

By waking up at or before a scheduled wakeup interval, the station andthe peer station can transmit data to each other during the scheduledwakeup intervals and enter a doze state during the non-wakeup intervals.In this way, the station and the peer station are not always fullypowered on to conserve power but yet the station and the peer stationcommunicate often enough to keep up with the data traffic.

FIG. 6 is a flow chart that illustrates a second embodiment of a methodof saving power for stations configured to communicate via a directlink. In FIG. 6, the method 600 includes blocks 610, 620, and 630. Inblock 610, a periodic wakeup schedule is negotiated by a station and apeer station. For example, the station may send a wakeup schedulerequest frame that defines a proposed periodic wakeup schedule.Specifically, the wakeup schedule request frame may contain a wakeupschedule field that defines a duration and a periodicity relative to ashared reference, such as the TBTT, as discussed above with respect tothe first embodiment illustrated in FIG. 5. The information included inthe wakeup schedule subfields may include a wakeup interval length and awakeup interval offset, as illustrated in Table 2. In response to thereceived wakeup schedule request frame, the peer station may propose adifferent periodic wakeup schedule in a wakeup schedule response frametransmitted to the station. Alternatively, the peer station may acceptor acknowledge the originally proposed periodic wakeup schedule in awakeup schedule response frame transmitted to the station. The stationmay then respond by accepting, acknowledging the different periodicwakeup schedule or by proposing another periodic wakeup schedule. Wakeupschedule request/response frames may be exchanged in this manner betweenthe station and the peer station until a proposed periodic wakeupschedule is accepted. Any other type of negotiation that results in awakeup schedule that is agreed upon by the station and the peer stationmay be implemented as well. Proposing a wakeup schedule to the peerstation by the station without allowing the option of rejecting ormodifying the proposed wakeup schedule by the peer station is alsoconsidered a negotiation in this context.

In block 620, a frame including a PM bit set is transmitted from thestation to the peer station. The frame including the PM bit set includesthe PM bit, which is illustrated in FIG. 4, set to 1 to indicate thatthe station is in a power save mode. In some embodiments, the frameincluding the PM bit set may be referred to as a trigger frame, and thetrigger frame may trigger a service period.

In block 630, the station wakes up at or before at least one of aplurality of scheduled wakeup intervals of the periodic wakeup schedulenegotiated by the station and the peer station in block 610. In otherwords, the station enters an awake mode at or before each scheduledwakeup interval.

By waking up at or before a scheduled wakeup interval, the station andthe peer station can transmit data to each other during the scheduledwakeup intervals and enter a doze state during the non-wakeup intervals.In this way, the station and the peer station are not always fullypowered on to conserve power but yet the station and the peer stationcommunicate often enough to keep up with the data traffic.

FIG. 7 is a flow chart that illustrates a third embodiment of a methodof saving power for stations configured to communicate via a directlink. In FIG. 7, the method 700 includes blocks 710, 720, and 730. Inblock 710, a schedule request frame including a PM bit set istransmitted from a station to a peer station over a direct link. Theschedule request frame defines a plurality of scheduled wakeupintervals. Specifically, the schedule request frame defines a durationand periodicity relative to a shared timing reference, such as the TBTTor TSF, as discussed above with respect to the first embodimentillustrated in FIG. 5. Information that may be included in the wakeupschedule subfields includes the wakeup interval length and the wakeupinterval offset, as illustrated in Table 3. The PM bit, which isillustrated in FIG. 4, in the schedule request frame is set to 1 toindicate that the station is in a power save mode. After transmittingthe schedule request frame including a PM bit set to 1, the station maypostpone entering the power save mode until a schedule response frame isreceived from the peer station. In other embodiments, after transmittingthe schedule request frame including a PM bit set, the station startswaking up according to the proposed wakeup schedule.

In block 720, a schedule response frame including a PM bit set istransmitted from the peer station to the station over the direct link,possibly after waiting for a proposed wakeup interval to occur. Theschedule response frame includes the PM bit set to 1 to indicate thatthe station is in a power save mode. In some embodiments, the scheduleresponse frame also indicates that the proposed wakeup schedule isaccepted or acknowledges the proposed wake up schedule. The wakeupschedule field illustrated in Table 2 may be omitted from the wakeupschedule response frame to indicate the wakeup schedule request frameincludes an acceptable wakeup schedule. The wakeup schedule fieldillustrated in Table 2 may also be included in the schedule responseframe, to indicate an alternative wakeup schedule.

In block 730, the station and the peer station wake up at or before aplurality of scheduled wakeup intervals. For example, the station andthe peer station both enter an awake mode at or before each scheduledwakeup interval of a plurality of scheduled wakeup intervals. Thestation and/or the peer station may have formerly been in a permanentdoze state.

By waking up at or before a scheduled wakeup interval, the station andthe peer station can transmit data to each other during the scheduledwakeup intervals and enter a doze state during the non-wakeup intervals.In this way, the station and the peer station are not always fullypowered on to conserve power but yet the station and the peer stationcommunicate often enough to keep up with the data traffic.

FIG. 8 is a flow chart that illustrates a fourth embodiment of a methodof saving power for stations configured to communicate via a directlink. In FIG. 8, the method 800 includes blocks 810, 820, and 830. Inblock 810, a station wakes up at or before a scheduled wakeup interval.In other words, the station enters an awake mode at or before ascheduled wakeup interval.

In block 820, a data frame is received over a direct link at the stationfrom a peer station during a scheduled wakeup interval. The data frameis sent during a service period that is started during a scheduledwakeup interval.

In block 830, the station remains awake at least until a frame includingan End of Service Period (EOSP) bit set is received from the peerstation. The frame including the EOSP bit set indicates that the serviceperiod is ending, and that the peer station will no longer be sendingdata frames for that service period to the station. In some embodiments,the station stays in an awake mode until a frame including an EOSP bitset is received, but enters a doze state before the scheduled wakeupinterval has elapsed. In some embodiments, the frame including an EOSPbit set to 1 is the first frame received during the scheduled wakeupinterval.

The Quality of Service (QoS) Control field, depicted in the MAC headerillustrated in FIG. 3, includes an EOSP field that can be used toindicate to a receiver that no further data is buffered for thatreceiver and that a service period is terminated. The QoS Control fieldis described in Table 4 below. For QoS Data and QoS Null frames, theEOSP field is present as bit 4 of the QoS Control field.

TABLE 4 QoS Control field Applicable Frame Bits (sub) Types 0-3 Bit 4Bits 5-6 Bit 7 Bits 8-15 QoS Data and QoS TID EOSP Ack Reserved ReservedNull frames sent over Policy the direct link

In the absence of traffic to be exchanged, the station remains awake forthe duration of the negotiated wakeup interval length as illustrated inTable 2. When traffic is exchanged, the station remains awake until theend of the service period, which may be shorter or longer than thewakeup interval length.

FIG. 9 is a flow chart that illustrates a fifth embodiment of a methodof saving power for stations configured to communicate via a directlink. In FIG. 9, the method 900 includes blocks 910, 920, and 930. Inblock 910, a station wakes up at or before a scheduled wakeup interval.In other words, the station enters an awake mode at or before eachscheduled wakeup interval.

In block 920, a data frame is received over a direct link at the stationfrom a peer station during a scheduled wakeup interval. The data frameis sent during a service period that is started during a scheduledwakeup interval.

In block 930, the station remains awake depending on whether traffic isbeing exchanged with the peer station. For example, if no furthertraffic is being exchanged with the peer station because the serviceperiod was terminated by the transmission by the station of a frame withthe EOSP bit set to 1, the station may enter a doze state after thescheduled wakeup interval has elapsed. If the service period will not beover before the scheduled wakeup interval has elapsed, the stationremains awake until the end of the service period (e.g., until thetraffic exchange is complete and the service period is terminated by atransmission by the station of a frame with the EOSP bit set to 1).

FIG. 10 is a flow chart that illustrates a sixth embodiment of a methodof saving power for stations configured to communicate via a directlink. In FIG. 10, the method 1000 includes blocks 1010, 1020, 1030, and1040. In block 1010, a station and a peer station wake up at or before ascheduled wakeup interval. For example, the station and the peer stationboth enter an awake mode at or before a scheduled wakeup interval.

In block 1020, a first data frame is received at the station from thepeer station during the scheduled wakeup interval over a direct link.The first data frame is received during a first service period duringthe scheduled wakeup interval.

In block 1030, a second data frame is received at the peer station fromthe station during the scheduled wakeup interval over the direct link.The second data frame is received during a second service period duringthe scheduled wakeup interval.

In block 1040, the station remains awake at least until a data frameincluding the EOSP bit set is received from the peer station.

FIG. 11 is a flow chart that illustrates a seventh embodiment of amethod of saving power for stations configured to communicate via adirect link. In FIG. 11, the method 1100 includes blocks 1111, 1120, and1130. In block 1111, a station wakes up at or before a scheduled wakeupinterval. In other words, the station enters an awake mode at or beforeeach scheduled wakeup interval. The station may have formerly been in adoze state.

In block 1120, a data frame is received at the station from the peerstation over a direct link during the scheduled wakeup interval. Inother words, while the station is in an awake mode, the station receivesa data frame from the peer station. Further, the data frame starts aservice period or is received during a service period.

In block 1130, the peer station remains awake at least until a frameincluding an EOSP bit set is transmitted to and received at the peerstation. The frame including the EOSP bit set indicates that the serviceperiod is ending, and that the peer station will no longer be sendingdata frames for that service period to the station. In some embodiments,the peer station stays in an awake mode until a frame including an EOSPbit set is received from the station, but enters a doze state before thescheduled wakeup interval has elapsed.

FIG. 12 is a flow chart that illustrates an eighth embodiment of amethod of saving power for stations configured to communicate via adirect link. In FIG. 12, the method 1200 includes blocks 1210, 1220, and1230. In block 1210, a station wakes up according to a negotiated wakeupschedule. In other words, the station enters an awake mode at or beforea scheduled wakeup interval included in a negotiated wakeup schedule.The station may have formerly been in a doze state. The negotiatedwakeup schedule may have been negotiated in a manner similar to thenegotiations described regarding block 610 of the second embodiment,which is discussed above.

In block 1220, no data frames are received at the station from the peerstation for a predetermined period of time, a predetermined number ofidle slots, or a predetermined number of schedule wakeup intervals. Insome embodiments, the no service period occurs for a predetermined timeor for a predetermined number of scheduled wakeup intervals. In someembodiments, the predetermined period of time may be 200 ms. In someembodiments, the predetermined time period is negotiable between thestation and the peer station. In some embodiments, the predeterminedtime period is determined at the station individually.

In block 1230, a schedule request frame that requests a termination ofthe negotiated wakeup schedule is transmitted from the station to thepeer station. In some embodiments, the station requests a termination ofthe negotiated wakeup schedule by proposing a different wakeup schedulein the schedule request frame that includes no scheduled wakeupintervals. The transmitted schedule request frame is illustrated inTable 1, and the wakeup schedule subfields indicate that there are noscheduled wakeup intervals. Specifically, the wakeup interval length maybe set to have a length of Ops, and the wakeup interval offset may beset to be Ops as well. Thus, according to the new different wakeupschedule, there are no scheduled wakeup intervals. A schedule requestframe proposing a termination of the wakeup schedule may be referred toas a termination frame.

By terminating the negotiated wakeup schedule, the station and the peerstation can both enter a doze state without periodically waking up forscheduled wakeup intervals. In this way, the time the station and thepeer station spend in a doze state can be increased to conserve power.

FIG. 13 is a flow chart that illustrates a ninth embodiment of a methodof saving power for stations configured to communicate via a directlink. In FIG. 13, the method 1300 includes blocks 1310, 1320, and 1330.In block 1310, a station wakes up according to a negotiated wakeupschedule. In other words, the station enters an awake mode at or beforea scheduled wakeup interval included in a negotiated wakeup schedule.The station may have formerly been in a doze state. The negotiatedwakeup schedule may have been negotiated in a manner similar to thenegotiations described regarding block 610 of the second embodiment,which is discussed above.

In block 1320, no data frames are received at the station over a directlink for a predetermined period of time or for a predetermined number ofscheduled wakeup intervals. In some embodiments, the predeterminedperiod of time is 200 ms. In other embodiments, the predetermined timeperiod is negotiable between the station and the peer station.

In block 1330, the negotiated wakeup schedule is terminated at thestation. In some embodiments, the station terminates the negotiatedwakeup schedule by proposing a different wakeup schedule that includesno scheduled wakeup intervals. The station proposes the different wakeupschedule by transmitting a wakeup schedule request frame to the peerstation. The transmitted wakeup schedule request frame is an indicationframe as discussed above regarding the first embodiment, and the wakeupschedule subfields indicate that there are no scheduled wakeupintervals. Specifically, the wakeup interval length is set to have alength of Ops, and the wakeup interval offset is set to be Ops as well.This proposed wakeup schedule of no wakeups may be accepted by the peerstation. Thus, since the negotiated wakeup schedule is terminated, thereare no scheduled wakeup intervals, and hence, the station can enter adoze state to conserve power. A schedule request frame proposing atermination of the wakeup schedule may be referred to as a terminationframe.

In other embodiments, the station will count a consecutive number ofscheduled wakeup intervals that have occurred during which no data framewas transmitted (and therefore no service period began). When thecounted number equals a predetermined number of scheduled wakeupintervals (which may be equal to 1), the station will terminate thenegotiated wakeup schedule and may enter a more sustained doze state toconserve power without sending a termination frame.

FIG. 14 is a flow chart that illustrates a tenth embodiment of a methodof saving power for stations configured to communicate via a directlink. In FIG. 14, the method 1400 includes blocks 1410, 1420, 1430, and1440. In block 1410, a frame destined for a peer station is received ata station. The frame may be an MDSU. The peer station may be in a powersave state without periodic wakeup with respect to the station when theframe destined for the peer station is received by the station, whichmay imply that it is unknown at the station if and when the peer stationis ready to receive a frame on the wireless medium.

In block 1420, an indication frame is sent from the station through anAP to the peer station, that causes a wakeup schedule to be set up andactivated at the station and the peer station. An exemplary indicationframe may include some or all of the information shown below in Table 5.

TABLE 5 Exemplary Indication Frame Fields Order Field Notes 1 LinkIdentifier identifies the direct link 2 AC_VO state indicates if AC_VOis empty (0) or not (1) 3 AC_VI state indicates if AC_VI is empty (0) ornot (0) 4 AC_BE state indicates if AC_BE is empty (0) or not (1) 5 AC_BKstate indicates if AC_BK is empty (0) or not (1) 6 Wakeup Scheduledefines a periodic wakeup schedule

The link identifier field of the exemplary indication frame in Table 5may identify a direct link through the station MAC address, the peerstation MAC address, and the basic service set identifier (BSSID), whichis the AP MAC address.

The access category (AC) state fields in Table 5 may be optionallypresent in the schedule request frame to indicate whether thecorresponding AC is empty (0) or non-empty (1). For example, asillustrated in Table 5, access category (AC) state fields AC_VO, AC_VI,AC_BE, AC_BK may be present. AC_VO is the access category for voice typetraffic; AC_VI is the access category for video type traffic; AC_BE isthe access category for best effort type traffic; and AC_BK is theaccess category for background type traffic.

The wakeup schedule field of the exemplary indication frame in Table 5defines a periodic wakeup schedule. The subfields of the wakeup schedulefield of the exemplary indication frame in Table 5 are the same as thesubfields shown in Table 2 regarding the wakeup schedule field of theexemplary wakeup schedule request frame. In fact, in some embodiments,the indication frame may be a wakeup schedule request frame. The wakeupinterval length subfield indicates the length of the wakeup interval.The wakeup interval offset subfield indicates the offset of the start ofthe wakeup interval relative to the TBTT or TSF. In some embodiments,the indication frame is sent when no wakeup schedule is currently activebetween the station and the peer station, and the peer station indicatedto the station that the peer station is in a power save mode.

In some embodiments, the indication frame is sent when no scheduledwakeup interval has occurred for at least a duration equal to anindication window. The indication window prevents the transmission ofthat too many indication frames and suppresses the transmission ofindication frames when a wakeup schedule is active.

The duration of the indication window is such that it is not too long tocause unwanted latency for buffered traffic and not too short togenerate too many indication frames. In some embodiments, the durationof the indication window is negotiable between a station and a peerstation. In some embodiments, the duration of the indication window isadjustable depending upon the inter-arrival time of MSDUs. For example,if the inter-arrival time of MSDUs in a stream exceeds the duration ofthe indication window, the duration of the indication window may beincreased to avoid that an indication frame is transmitted for eachMSDU. Likewise, if the inter-arrival time of MSDUs in a stream fallshort of the duration of the indication window, the duration of theindication window may be decreased to reduce the latency that isexperienced by the MSDUs before they get transmitted to the peerstation. In some embodiments, the duration of the indication window isfixed or predetermined. For example, the duration of the indicationwindow may be 200 ms.

In block 1430, an indication response frame is sent from the peerstation through the AP to the station. The indication response frame issent in response to receiving the indication frame at the peer station.The indication response frame sets up or acknowledges the wakeupschedule to be set up and activated at the station and the peer station.In some embodiments, the schedule response frame also indicates that theproposed wakeup schedule is accepted or acknowledges the proposed wakeup schedule. In some embodiments, the indication frame does not containa proposed wakeup schedule and the wakeup schedule is set by theindication response frame. The wakeup schedule field illustrated inTable 3 may be omitted from the schedule response frame to indicate thewakeup schedule request frame includes an acceptable wakeup schedule. Anexemplary indication response frame includes the information shown inTable 6.

TABLE 6 Exemplary Indication Response Frame Fields Order Fields Notes 1Link Identifier The Link Identifier field identifies the direct link 2Wakeup The Wakeup Schedule field defines a periodic Schedule wakeupschedule

The link identifier field may identify a direct link through the stationMAC address, the peer station MAC address and the basic service setidentifier (BSSID), which is the AP MAC address. The wakeup schedulefield may be omitted from the wakeup schedule response frame when thewakeup schedule request frame included an acceptable wakeup schedule. Insome embodiments, the indication response frame may also be a wakeupschedule response frame.

In block 1440, a data frame is sent from the station to the peer stationover a direct link during a scheduled wakeup interval. In other words,the data frame is sent to the peer station when the peer station is inan awake mode, which is during a scheduled wakeup interval.

FIG. 15 is a flow chart that illustrates an eleventh embodiment of amethod of saving power for stations configured to communicate via adirect link. In FIG. 15, the method 1500 includes blocks 1510, 1520,1530, 1540, 1550, 1560, 1570 and 1580. In block 1510, a frame destinedfor a peer station is received at a station. The frame may be an MDSU.The peer station may be in a power save state without periodic wakeupwhen the frame destined for the peer station is received by the station,which may imply that it is unknown at the station if and when the peerstation is ready to receive a frame on the wireless medium. In block1520, the received frame for the peer station is buffered at thestation. For example, the received frame may be placed in a queue, suchas an access category (AC), to wait until the peer station is in anawake mode and able to receive the received frame.

In block 1530, an indication frame is sent from the station through theAP to the peer station when no scheduled wakeup interval has occurredfor a duration equal to at least an indication window. The indicationframe may be transmitted when an indication window has expired withoutthe occurrence of a scheduled wakeup interval. The indication windowprevents the transmission of too many indication frames and suppressesthe transmission of indication frames when a wakeup schedule is active.In some embodiments, an indication frame may be transmitted only when noindication frame has been transmitted for at least a duration equal toan indication window.

The duration of the indication window is such that it is not too long tocause unwanted latency for buffered traffic and not too short togenerate too many indication frames. In some embodiments, the durationof the indication window is negotiable between a station and a peerstation. In some embodiments, the duration of the indication window isadjustable depending upon the inter-arrival time of MSDUs. For example,if the inter-arrival time of MSDUs in a stream exceeds the duration ofthe indication window, the duration of the indication window may beincreased. Likewise, if the inter-arrival time of MSDUs in a stream fallshort of the duration of the indication window, the duration of theindication window may be decreased. In some embodiments, the duration ofthe indication window is fixed or predetermined. For example, theduration of the indication window may be 200 ms.

In block 1540, an indication response frame is sent from the peerstation through the AP to the station. The indication response frameindicates that the wakeup schedule is accepted. The indication responseframe may be formed as discussed above regarding block 530. In block1550, the peer station wakes up according to the accepted wakeupschedule. In other words, the peer station enters an awake modeaccording to the scheduled wakeup intervals of the accepted wakeupschedule. In some embodiments, the station enters an awake stateimmediately after sending the indication frame in block 1530 andpossibly before the station receives the indication response frame sentfrom the peer station. In other embodiments, the station enters an awakestate according to the wakeup schedule included in the transmittedindication frame, immediately after sending the indication frame inblock 1530.

In block 1560, the indication response frame is received at the stationfrom the peer station. Hence, the station determines that the peerstation is aware of the accepted wakeup schedule and that the peerstation is waking up according to the accepted wakeup schedule. In someembodiments, when the station wakes up according to the wakeup scheduleincluded in the transmitted indication frame immediately aftertransmitting the indication frame in block 1530, the peer station maytransmit the indication response frame to the station via the directlink during a scheduled wakeup interval. In block 1570, the stationwakes up according to the accepted wakeup schedule. In other words, thestation enters an awake mode according to the scheduled wakeup intervalsof the accepted wakeup schedule. In block 1580, the received framebuffered for the peer station in block 1520 is transmitted from thestation to the peer station via a direct link. The received framebuffered for the peer station is transmitted from the station to thepeer station during a service period.

In this way, the received frame buffered for the peer station was savedfor sending to the peer station until a time in which the peer stationwould be in an awake mode and ready to receive the received frame. Bybuffering the received frame at the station and sending the receivedframe to the peer station during a scheduled wakeup interval, the timethe peer station can spend in a doze state is increased, and thus, poweris conserved.

FIG. 16 is a flow chart that illustrates a twelfth embodiment of amethod of saving power for stations configured to communicate via adirect link. In FIG. 16, the method 1600 includes blocks 1610, 1620,1630, 1640, and 1650. In block 1610, a frame destined for a peer stationis received at a station. The frame may be an MDSU. The peer station maybe in a power save state without periodic wakeup when the frame destinedfor the peer station is received by the station, which may imply that itis unknown at the station if and when the peer station is ready toreceive a frame on the wireless medium.

In block 1620, the received frame for the peer station is buffered atthe station. For example, the received frame may be placed in a queue,such as an access category (AC), to wait until the peer station is in anawake mode and able to receive the received frame. In block 1630, awakeup schedule is negotiated between the station and the peer stationwhen no wakeup interval has occurred for a duration equal to at least anindication window. The wakeup schedule request frame may be transmittedwhen an indication window has expired. The indication window preventsthe transmission of too many indication frames and suppresses thetransmission of indication frames when a wakeup schedule is active. Inanother embodiment, a wakeup schedule is negotiated when no wakeupschedule is currently active between the station and the peer station.

The duration of the indication window is such that it is not too long tocause unwanted latency for buffered traffic and not too short togenerate too many indication frames. In some embodiments, the durationof the indication window is adjustable depending upon the inter-arrivaltime of MSDUs. For example, if the inter-arrival time of MSDUs in astream exceeds the duration of the indication window, the duration ofthe indication window may be increased. Likewise, if the inter-arrivaltime of MSDUs in a stream falls short of the duration of the indicationwindow, the duration of the indication window may be decreased. In someembodiments, the duration of the indication window is fixed orpredetermined as a result of the negotiated wakeup schedule. Forexample, the negotiated duration of the indication window may be 200 ms.

In block 1640, the station and the peer station wake up according to thenegotiated wake up schedule. In other words, the station and the peerstation enter an awake mode at scheduled wakeup intervals according tothe negotiated wakeup schedule. In block 1650, the received framebuffered for the peer station is transmitted from the station to thepeer station via direct link during a wakeup interval of the negotiatedwakeup schedule.

In this way, the received frame buffered for the peer station was savedfor sending to the peer station until a time in which the peer stationwould be in an awake mode and ready to receive the received frame. Bybuffering the received frame at the station and sending the receivedframe to the peer station during a scheduled wakeup interval, the timethe peer station can spend in a doze state is increased, and thus, poweris conserved.

FIG. 17 is a flow chart that illustrates a thirteenth embodiment of amethod of saving power for stations configured to communicate via adirect link. In FIG. 17, the method 1700 includes blocks 1710, and 1720.In block 1710, a station and a peer station wake up before a scheduledwakeup interval. The scheduled wakeup interval is defined relative to acommon timing reference at the station and the peer station. In someembodiments, the common timing reference is a target beacon transmissiontime (TBTT) associated with a beacon. The beacon is delivered by anaccess point (AP), which is associated with the station and the peerstation. The scheduled wakeup interval is one of a plurality ofscheduled wakeup intervals included in a wakeup schedule, which may beperiodic.

In block 1720, in the absence of a service period, the station and thepeer station stay awake until at least a predefined time period haselapsed or a predefined number of idle slots have elapsed.

In some embodiments, the station and the peer station stay awake until aservice period has ended. In some embodiments, the station and the peerstation enter a doze state when at least a predefined time period haselapsed during which no service period has occurred between the stationand the peer station.

In some embodiments, the station and the peer station enter a doze statewhen at least a predefined number of idle slots have elapsed and noservice period has occurred between the station and the peer stationduring the duration of the predefined number of idle slots that elapsed.In some embodiments, the idle time slots are determined according to adistributed channel access protocol.

In some embodiments, the method 1700 further includes the waking upbeing terminated when a predefined number of scheduled wakeup intervalshave elapsed during which no service period has occurred. Further, insome embodiments, the waking up is terminated by the transmission of atermination frame by the station or the peer station.

FIG. 18 is a flow chart that illustrates a fourteenth embodiment of amethod of saving power for stations configured to communicate via adirect link. In FIG. 18, the method 1800 includes blocks 1810, 1820 and1830. In block 1810, an indication frame is sent from a station via anAP to a peer station that causes a wakeup schedule to be set up andactivated at the station and the peer station. The indication frame issent when the station and the peer station are in a power save mode andno wakeup schedule is currently active between the station and the peerstation.

In block 1820, a wakeup schedule is negotiated between the station andthe peer station. In other words, the station and the peer stationnegotiate a wakeup schedule. In block 1830, the station wakes up at orbefore at least one of a plurality of scheduled wakeup intervals of thenegotiated wakeup schedule.

FIG. 19 is a flow chart that illustrates a fifteenth embodiment of amethod of saving power for stations configured to communicate via adirect link. In FIG. 19, the method 1900 includes blocks 1910, 1920, and1930. In block 1910, an indication frame is sent from the station via adirect link to a peer station that causes a wakeup schedule to be set upat the station and the peer station. The indication frame is sent whenthe station and the peer station are not in a power save mode and nowakeup schedule is currently active between the station and the peerstation.

In block 1920, a wakeup schedule is negotiated between the station andthe peer station. In other words, the station and the peer stationnegotiate a wakeup schedule. In block 1930, a frame with a PM bit set to1 is transmitted from the peer station or the station, respectively, andthe station or the peer station activates the negotiated wakeupschedule.

In the various embodiments discussed above with respect to FIGS. 5-19,traffic for an AC may be routed over the direct link while traffic foranother AC may be routed through the AP. If an AC carries traffic thathas high duty cycle relative to the traffic routed through another AC,it may be useful to route the traffic having the higher duty cycle overthe direct link while the traffic having the lower duty cycle is routedthrough the AP. Video (VI) and voice (VO) traffic may have a high dutycycle relative to background (BK) and best effort (BE), and traffic forAC_VI and AC_VO is routed through the direct link while traffic forAC_BK and AC_BE is routed through the AP.

The various embodiments discussed above with respect to FIGS. 5-19 maybe used when the duty cycle is still low enough for idle periods to beused to save power. When the duty cycle exceeds a certain threshold (forinstance when the duty cycle is higher than approximately 70%), thestations may decide to always be awake. A high duty cycle may also causethe service period to extend into the next scheduled wakeup, in whichcase there is no time to enter a doze state while a periodic wakeupschedule is still active and the stations are still in a power savemode.

In the various embodiments discussed above with respect to FIGS. 5-19,one or more additional direct links may be present. For example, astation may communicate over a first direct link to a first peerstation, and the station may also communicate over a second direct linkto a second peer station. Further, the station may communicate over thefirst direct link to the first peer station according to a first wakeupschedule, and the station may communicate over the second direct link tothe second peer station according to a second wakeup schedule. In orderto further conserve power at the station, the first wakeup schedule andthe second wakeup schedule may overlap or be the same. The station maynegotiate the first wakeup schedule with the first peer station and thesecond wakeup schedule with the second peer station to produce a firstwakeup schedule and a second wakeup schedule that overlap or are thesame.

In the various embodiments discussed above with respect to FIGS. 5-19,where applicable, the wakeup schedule may be negotiated as part of thedirect link setup handshake. In some embodiments, the station and/or thepeer station may indicate to the other station whether the stationand/or the peer station will be in a power save mode when the directlink setup handshake completes. This indication is similar to theexchange of frames with the PM bit set to 1, except that the informationis piggybacked on the setup handshake. A wakeup schedule may benegotiated as part of the direct link setup handshake, or the wakeupschedule may be negotiated when a traffic stream will be transmittedover the direct link in the near future, initiated for instance by ahigher layer protocol or application.

Any process descriptions or blocks in flow diagrams shown in FIGS. 5-19should be understood as representing modules, segments, or portions ofcode which include one or more executable instructions for implementingspecific logical functions or steps in the process, and alternateimplementations are included within the scope of the embodimentsdescribed herein in which functions may be executed out of order fromthat shown or discussed, including substantially concurrently or inreverse order, depending on the functionality involved, as would beunderstood by those reasonably skilled in the art. Additionally, themethods illustrated in the flow charts of FIGS. 5-19 are not limited tothe system embodiments shown in FIGS. 1 and 2, but may be extended toother architectures and systems as should be appreciated by one havingordinary skill in the art in the context of this disclosure.

It should be emphasized that the above-described embodiments are merelypossible examples of implementations, merely set forth for a clearunderstanding of the principles of the disclosure. Many variations andmodifications may be made to the above-described embodiment(s) withoutdeparting substantially from the scope of the disclosure. All suchmodifications and variations are intended to be included herein withinthe scope of this disclosure.

At least the following is claimed:
 1. A method comprising: determining awakeup schedule; and communicating the wakeup schedule between a firststation and a second station, the wakeup schedule scheduling a pluralityof fixed length durations, each duration comprising a dynamic wakeupinterval, wherein in the absence of a service period, the dynamic wakeupinterval comprises a fixed number of idle slots and the total length ofthe dynamic wakeup interval depends.
 2. The method of claim 1, whereinthe number of idle slots elapse according to a distributed channelaccess method.
 3. The method of claim 2, wherein the distributed channelaccess method is the enhanced distributed channel access (EDCA) method.4. The method of claim 1, wherein a first wakeup interval ends after afixed time period and before the number of idle slots elapse.
 5. Themethod of claim 1, wherein the wakeup schedule is defined relative to ashared time reference.
 6. The method of claim 5, wherein the shared timereference corresponds to one of a timing synchronization function (TSF)or a target beacon transmission time (TBTT).